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            <div><h3 class="title">
                <a name="asio.reference.WaitTraits"></a><a class="link" href="WaitTraits.html"
                                                           title="Wait traits requirements">Wait traits requirements</a>
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    <p>
        The <code class="computeroutput"><span class="identifier">basic_waitable_timer</span></code>
        template uses wait traits to allow programs to customize <code class="computeroutput"><span class="identifier">wait</span></code>
        and <code class="computeroutput"><span class="identifier">async_wait</span></code> behavior.
        [<span class="emphasis"><em>Note:</em></span> Possible uses of wait traits include:<br> — To
        enable timers based on non-realtime clocks.<br> — Determining how quickly
        wallclock-based timers respond to system time changes.<br> — Correcting for
        errors or rounding timeouts to boundaries.<br> — Preventing duration overflow.
        That is, a program may set a timer's expiry <code class="computeroutput"><span
            class="identifier">e</span></code>
        to be <code class="computeroutput"><span class="identifier">Clock</span><span class="special">::</span><span
            class="identifier">max</span><span class="special">()</span></code> (meaning
        never reached) or <code class="computeroutput"><span class="identifier">Clock</span><span
            class="special">::</span><span class="identifier">min</span><span class="special">()</span></code> (meaning
        always in the past). As a result, computing the duration until timer expiry
        as <code class="computeroutput"><span class="identifier">e</span> <span class="special">-</span>
        <span class="identifier">Clock</span><span class="special">::</span><span class="identifier">now</span><span
                class="special">()</span></code> may
        cause overflow. —<span class="emphasis"><em>end note</em></span>]
    </p>
    <p>
        For a type <code class="computeroutput"><span class="identifier">Clock</span></code> meeting
        the <code class="computeroutput"><span class="identifier">Clock</span></code> requirements (C++Std
        [time.clock.req]), a type <code class="computeroutput"><span class="identifier">X</span></code>
        meets the <code class="computeroutput"><span class="identifier">WaitTraits</span></code> requirements
        if it satisfies the requirements listed below.
    </p>
    <p>
        In the table below, <code class="computeroutput"><span class="identifier">t</span></code> denotes
        a (possibly const) value of type <code class="computeroutput"><span class="identifier">Clock</span><span
            class="special">::</span><span class="identifier">time_point</span></code>;
        and <code class="computeroutput"><span class="identifier">d</span></code> denotes a (possibly
        const) value of type <code class="computeroutput"><span class="identifier">Clock</span><span
            class="special">::</span><span class="identifier">duration</span></code>.
    </p>
    <div class="table">
        <a name="asio.reference.WaitTraits.t0"></a>
        <p class="title"><b>Table 35. WaitTraits requirements</b></p>
        <div class="table-contents">
            <table class="table" summary="WaitTraits requirements">
                <colgroup>
                    <col>
                    <col>
                    <col>
                </colgroup>
                <thead>
                <tr>
                    <th>
                        <p>
                            expression
                        </p>
                    </th>
                    <th>
                        <p>
                            return type
                        </p>
                    </th>
                    <th>
                        <p>
                            assertion/note<br> pre/post-condition
                        </p>
                    </th>
                </tr>
                </thead>
                <tbody>
                <tr>
                    <td>
                        <p>
                            <code class="computeroutput"><span class="identifier">X</span><span
                                    class="special">::</span><span class="identifier">to_wait_duration</span><span
                                    class="special">(</span><span class="identifier">d</span><span
                                    class="special">)</span></code>
                        </p>
                    </td>
                    <td>
                        <p>
                            <code class="computeroutput"><span class="identifier">Clock</span><span
                                    class="special">::</span><span class="identifier">duration</span></code>
                        </p>
                    </td>
                    <td>
                        <p>
                            Returns a <code class="computeroutput"><span class="identifier">Clock</span><span
                                class="special">::</span><span class="identifier">duration</span></code>
                            value to be used in a <code class="computeroutput"><span
                                class="identifier">wait</span></code>
                            or <code class="computeroutput"><span class="identifier">async_wait</span></code> operation.
                            [<span class="emphasis"><em>Note:</em></span> The return value is typically representative
                            of the duration <code class="computeroutput"><span class="identifier">d</span></code>.
                            —<span class="emphasis"><em>end note</em></span>]
                        </p>
                    </td>
                </tr>
                <tr>
                    <td>
                        <p>
                            <code class="computeroutput"><span class="identifier">X</span><span
                                    class="special">::</span><span class="identifier">to_wait_duration</span><span
                                    class="special">(</span><span class="identifier">t</span><span
                                    class="special">)</span></code>
                        </p>
                    </td>
                    <td>
                        <p>
                            <code class="computeroutput"><span class="identifier">Clock</span><span
                                    class="special">::</span><span class="identifier">duration</span></code>
                        </p>
                    </td>
                    <td>
                        <p>
                            Returns a <code class="computeroutput"><span class="identifier">Clock</span><span
                                class="special">::</span><span class="identifier">duration</span></code>
                            value to be used in a <code class="computeroutput"><span
                                class="identifier">wait</span></code>
                            or <code class="computeroutput"><span class="identifier">async_wait</span></code> operation.
                            [<span class="emphasis"><em>Note:</em></span> The return value is typically representative
                            of the duration from <code class="computeroutput"><span class="identifier">Clock</span><span
                                class="special">::</span><span class="identifier">now</span><span
                                class="special">()</span></code> until the time point <code class="computeroutput"><span
                                class="identifier">t</span></code>. —<span class="emphasis"><em>end note</em></span>]
                        </p>
                    </td>
                </tr>
                </tbody>
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